Spinal osteosynthesis device and preparation method

ABSTRACT

A spinal internal implantation device for osteosynthesis has one or more bars for supporting for moving the spine and at least one implant for connecting the bars and vertebrae. The implant includes a blown anchor attached to a body of the implant and a fixation arrangement for the bars. The fixation arrangement includes a clamp for clamping the bar against internal walls of a channel formed in the body of the implant. At least part of the length of the bars includes a transversal bearing structure that is a cross-section of the bars having at least one flat part of a part having a lower forepost convexity than the rest of the cross section.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.13/873,190 filed Apr. 29, 2013, and issuing as U.S. Pat. No. 9,763,699on Sep. 19, 2017, which is a continuation of U.S. patent applicationSer. No. 12/409,327 filed Mar. 23, 2009, and issuing as U.S. Pat. No.8,430,915 on Apr. 30, 2013, which is a continuation of U.S. patentapplication Ser. No. 10/473,999 filed Oct. 6, 2003, and issuing as U.S.Pat. No. 7,507,248 on Mar. 24, 2009, which is a National Stage Entry ofInternational Application PCT/IB02/02827, filed Apr. 3, 2002, whichclaims priority to French Patent Application No. 0104717, filed Apr. 6,2001.

BACKGROUND

The present invention relates to an osteosynthesis device, particularlyfor spinal support or correction, that can be used in particular forinternal implantation.

For spinal support or correction, a device comprising one or moresupport bars positioned along the spinal column is used, and fixed tocertain vertebrae by implants. Said implants are fixed at one end to thebars and at the other end to the vertebrae by bone anchorage means,composed of a hook supported by a vertebra or of a threaded part screwedinside the vertebra itself, for example at the pedicle.

In such devices, it is known to use bars inserted into the body of theimplant via an opening, either simply through the implant or in the formof a channel opening onto a side, said channel possibly opening onto theside or rear (on the top of the implant).

In the case of a closed type implant, the insertion of the bar must mostfrequently be carried out after the fixation of the implants, whichrequires the delicate operation of deforming the bar as it is insertedinto the different implants.

In the case of an implant with a side or rear opening, the bar-implantfixation may be obtained by means of an intermediate part referred to asa clamp. Said clamp is formed from a ring which is inserted around thebar and fixed to it by a clamping screw, said clamp in turn beinginserted into the opening of the implant longitudinally along the axisof the bar. Once the clamp is inserted longitudinally in the implant, asin patent FR 2 545 350, the clamping is obtained by a conical shank andsecured by an additional part referred to as a safety lock. Failing asafety lock, as in patent EP 0 392 927, the clamping is secured by twoadditional screws clamped onto the bar via the clamp and the body of theimplant.

Another possibility consists of inserting the bar directly into animplant with a rear open channel, as in patent FR 2 680 461, andclamping this bar with a threaded plug securing the bar by means of acurved blade to provide a satisfactory contact surface.

In both cases, this assembly of several parts is intended to ensure thereliability of the clamping, but represents a complexity and size liableto render implantation delicate, particularly at the junction of thelumbar and sacral regions where only a small amount of space isavailable due to anatomical conditions. The presence of small parts toassemble during the operation involves the disadvantage of more delicatemanipulations and the risk of said small parts being disseminated in theoperative field.

SUMMARY

An aim of the present invention is to remedy the drawbacks of the priorart by providing an osteosynthesis device enabling easier adjustment onthe operative site and more rapid implantation.

Another aim is to provide a more compact osteosynthesis device.

Another aim is to provide an osteosynthesis device comprising a reducednumber of separate parts during implantation.

Another aim is to provide an osteosynthesis device wherein the clampingor fastening shows improved reliability.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention, with its characteristics and advantages, will be seenmore clearly upon reading the description with reference to the appendedfigures wherein:

FIG. 1 is a rear view on the spine of an osteosynthesis device accordingto the invention, in the case of pedicular screw implants;

FIG. 2 is a partial side view of the region comprising the fixation of abar to an implant, at the stage where the bar is presented at the entryof the opening of the implant and where the clamping screw is pre-fittedin the implant;

FIGS. 3a and 5 are section side views of a device according to theinvention, at the axis of an implant, in an embodiment using a barcomprising a single flat part and for two different bar thicknesses;

FIG. 3b is a sectional side view of a device according to the invention,at the axis of an implant, in an embodiment comprising a polyaxialclamping screw;

FIG. 4a is a side view of a device according to the invention, at theaxis of an implant, in an embodiment using a bar comprising two flatparts;

FIG. 4b is a side view of a device according to the invention, at theaxis of an implant, in an embodiment using a bar comprising one flatpart and an implant comprising an inclined plane surface;

FIG. 6 is a side and top view of an implant according to the invention,in an embodiment using a bar comprising an end with no flat part, in thecase of a screw implant;

FIG. 7 is a sectional side view of a device according to the invention,at the axis of an implant, in an embodiment using a spherical headclamping screw clamping a bar comprising a recess or a circularcross-section groove complementary to the clamping face; and

FIG. 8 is a sectional side view of a device according to the invention,at the axis of an implant, in an embodiment using a spherical headclamping screw clamping a bar comprising a recess or a circularcross-section groove of a radius greater than that of the clamping face.

DETAILED DESCRIPTION OF THE DRAWINGS

The osteosynthesis device according to the invention uses the principlesof the prior art in terms of the possible application. It can be adaptedto screw or hook implants and will be represented here in the case ofscrew, or pedicular screw, implants. Such a device type may alsocomprise other components, such as transversal connection bars, notdescribed here but which may be included in the device according to theinvention. Due to its advantages in terms of size and easy implantationin reduced spaces, such a device is particularly suitable for entirelyinternal fitting, i.e. with no part protruding outside the epidermisafter the operation. This most frequently consists of a permanent deviceor one to be kept for a long time.

In an embodiment represented in FIGS. 2, 3 a and 5, the bar 2 has arounded cross-section comprising a flat part 21. Said flat part forms atransversal bearing surface, i.e. enabling clamping by supporting theclamping means on said surface, in a direction approximatelyperpendicular to the longitudinal axis of the bar 2. In its partcomprising the fixation means to the bar 2, the implant 3 comprises anopening in the form of a channel 32 passing through the implant alongthe axis of the bar. Said channel is open on one side of the implant andcomprises in one of its edges clamping means moving along an axisperpendicular to the axis of the channel and the bar 2.

Once inserted into the channel 32 of the implant 3, the bar is held byclamping against an internal wall 320 of the channel using clampingmeans, said means possibly being a clamping screw 31 co-operating with athreaded hole. In the embodiments illustrated in FIGS. 1 to 6, theclamping screw 31 comprises a plane part 310 at its end pressing on theflat part 31 of the bar. As a general rule, said clamping screw mayadvantageously be of a set screw type so as to minimize its size whileretaining the possibility of a long movement along its axis. Said screwcomprises gripping means, such as an upper face comprising a recess 312,FIGS. 7 and 8, capable of co-operating with a maneuvering or clampingtool, for example a hexagon socket recess.

In the embodiments described here, the body of the implant is attachedto the bone anchorage means, whether they consist of a threaded part(FIG. 6) or one or more hooks (not shown). In this case, the body of theimplant itself comprises the clamping means and receives the supportbar(s) 2, by direct contact or via intermediate support parts such asrings or distance sleeves.

In the embodiment described here, the clamping screw 31 is screwed intoa threaded hole passing through the top edge of the channel 32 and doesnot overlap onto the opening of said channel and therefore does notobstruct the insertion of the bar 2. Therefore, the clamping screw 31can be pre-fitted in the implant, thus decreasing the operations duringthe intervention, the operating time and the risk of the part being lostin the operative field.

Due to the plane contact between the clamping screw 31 and the bar 2, itis possible to use several types of bars, of different thicknesses e1,FIG. 3; e2, FIG. 5, in the same implant model, provided that thecross-section of the bar 2 is of a shape capable of co-operating withthe lower wall 320 of the implant channel. Indeed, due to the planenature of the contact surface 21 of the bar, the clamping screw 31 willclamp the bar 2 in the same way, irrespective of its thickness, providedthat its travel is sufficient to come into contact with the flat part21. Therefore, it is possible to have different bar thicknesses, andtherefore different rigidities, for the same implant model, whichreduces the stock and type of productions required to cover allrequirements. It is also possible to modify rigidity by changing the barduring the operation or during a subsequent operation according to theperformances obtained, without having to change the implants, whichcould represent an injury or additional damage to the vertebrae.

In another embodiment represented in FIG. 4a , the bar 2 comprises asecond flat part 22 opposite the first flat part 21 and approximatelyparallel to said part, said second flat part 22 forming a bearingsurface on the bottom face 320 of the channel 32 of the implant 3. Inthis arrangement, by means of its co-operation with the wall 320 of thechannel, the second flat part 22 of the bar helps ensure the stabilityand centering of said bar in the channel 32 of the implant duringclamping to ensure that the clamping screw 31 is indeed restingperpendicularly on the flat part 21 and therefore provides the bestclamping possible. Through this increased stability, this arrangementalso ensures improved subsequent reliability of the clamping, bypreventing the bar 2 from pivoting around its axis under the effect offorces or vibrations, which would be liable to cause the loosening ofthe assembly.

In one embodiment, the channel 32 receiving the bar 2 in the implant 3is of a shape enabling the extension of the bar along an outwarddirection d32 forming a non-null angle a with a plane perpendicular tothe axis of the clamping means 31. To prevent any untimely escape of thebar from the implant, said angle a is oriented in the direction wherethe outward direction d32 of the bar forms an acute angle with theloosening direction d31 of the clamping means. This means that theclamping means 31 must move in the loosening direction d31 for the barto be able to move d32 to the channel outlet.

In one embodiment represented in FIG. 3b , the clamping screw 31comprises a plane bearing surface 310 mounted on a ball joint 311,enabling perfectly flat support on the bar, even if the flat part is notexactly perpendicular to the axis of said clamping screw, in particularwhen the axes of the different implants are not perfectly parallel. Thepermissible angle a31 of inclination may for example be of the order of20 degrees.

The clamping means may be immobilized by any known means, such as glue,the plastic deformation at one or more points of the surfacesco-operating for their movement, or the presence of elasticallydeformable substances in the threading such as a “Nyl′stop” type lockingring. The only micro-movements remaining possible for the bar are then,at the most, limited to the plane perpendicular to the axis d31 of theclamping means. The movements in this plane, particularly when movingfrom the base of the channel, are themselves restricted by a part of thebottom edge of the channel, forming an upward nose 321 opposing thesemovements.

In one embodiment represented in FIG. 4b , the bar 2 comprises a flatpart 22 which co-operates with the inner wall 320 of the channel 32 ofthe implant forming a plane surface, thus ensuring the stability andcentering of said bar in the channel 32 of the implant during theclamping of the clamping screw 31. Said plane surface 320 of the implantforms a non-null angle b with a plane perpendicular to the axis d31 ofthe clamping means. So as to prevent any untimely escape of the bar fromthe implant, said angle b is oriented in the direction where the outwarddirection d32 of the bar forms an acute angle with the looseningdirection d31 of the clamping means. This means that the clamping means31 must move in the loosening direction d31 for the bar to be able tomove d32 to the channel outlet.

In one embodiment illustrated in FIG. 6, the support bar 2 comprises oneend, or two, comprising no flat part 21. The end of the flat part inthis case forms a shoulder 23 which ensures that the bar 2 does notescape from the implant in a direction longitudinal to said bar. Due tothis safety device, it is possible only to allow a very short length ofbar 2 to protrude from the implant, which reduces the size of theoverall device and improves its implantation possibilities at pointswhere anatomical conditions allow little space.

In one embodiment represented in FIG. 6, the implant 3 comprises boneanchorage means composed of one part 33 tapered and threaded in a knownway, the bar fixation means and clamping means 31 are in this caselocated in the end opposite the bone anchorage means. In thisembodiment, the axis d31 of the clamping means is parallel to the axisd33 of the bone anchorage means, the clamping being carried out bymoving closer to the threaded part, referred to here as the lower partof the implant 3. So as to limit the size of the implant, the axis ofthe clamping means may be offset by moving away from the inlet of thechannel 32 to insert the bar 2 in the implant. In the same way, the topedge of the channel comprises a recess r1 in relation to the bottom edgein its projection along the axis d33 of the implant. Said recess r1could typically be of the order of 2 mm. So as to provide sufficientclamping, the nose 321 formed by the bottom end of the channel 32protrudes upwards by a determined height r2 in relation to the planeperpendicular to the axis d31 of the clamping means and via the bottompart of the wall 320 which supports the bar 2 during clamping. Saidheight r2 could typically be of the order of 2 mm.

For the implantation of an osteosynthesis device according to the methodaccording to the invention, several types of implants, for examplescrewed or comprising a hook, may be used.

In the case (represented in FIG. 1) of screwed implants, thisimplantation may be carried out in the part of the vertebra referred toas the pedicle. This type of surgical intervention comprises in thiscase a step consisting of fixing by screwing the part of the implant 3provided with a screw pitch 33 on the vertebrae V, for example twoimplants on each of five vertebrae, by aligning the directions of theirrespective channels upwards.

During a surgical intervention, if an osteosynthesis device is implantedusing the method according to the invention, the use of bars 2comprising one or more flat parts 21, 22 enables said bars to offer adetermined flexibility along a direction perpendicular to said planefaces. Said flexibility is important when bending the bars, necessary toadapt the entire device to the patient's conformation and themodifications that need to be made. The presence of said plane facesalso enables the bars to comprise a plane surface on part of theirlength to comprise accurate implant dimensional references orpositioning references.

Due to the fact that implants of the same model can accept several barthicknesses e1, e2, it will be possible to modify the choice of barrigidity after fixing the implants, without needing to extract saidimplants from the vertebrae to insert others, therefore also withoutdamaging the vertebrae further in the case of screwed implants.

In a following step of a method according to the invention (representedin FIG. 2), the arrangement of the opening of the channel 32 of theimplant 3 makes it possible to insert the bar 2 in a simple lateralmovement, without requiring a longitudinal movement along the axis ofthe bar as in the case of a clamp.

Since the clamping screw 31 is already in place in the implant 3, theclamping can be carried out without assembling additional parts. Sincesaid clamping screw is supported by a plane part 310 on a plane surface21 of the bar, the contact surface enabling the clamping will be largerthan on a round cross-section bar, directly ensuring high reliability ofthe connection. Once the clamping screw is in place, the raising of thebottom edge of the channel 32 in the form of a nose 321 prevents anylateral movement of the bar outside the channel.

The clamping may be carried out in several stages, a first progressionof the clamping screw making it possible to hold the bar in the implantwhile allowing freedom of longitudinal movements to adjust the positionof the implants on the bar, as required. These adjustments may becomposed of a positioning of the implants at different distances fromthe end of the bar, to adjust the position of the spine in a sagittalplane, i.e. in different positions varying in terms of arching(lordosis) or curvature (cyphosis). Said adjustment may also comprisedifferences in positioning between the implants of each of two barsarranged at either side of the spine, to adjust the position of thespine in a lateral plane, i.e. in different curvatures inclined tovarying degrees on one side of the body or in relation to the pelvis.

Once the desired relative positions of the different components of thedevices and the spine have been obtained, the bar will be clampedcompletely in the implant in another step, as required and according tothe progress of the surgical intervention, by completely clamping theclamping screw on the flat part 21 of the bar.

The method according to the invention, by reducing the complexity of theassembly, makes it possible in this way to reduce implantationdifficulties, rendering the intervention shorter, less tiring for theoperative personnel and less traumatizing for the patient. By reducingthe size of the device without affecting the reliability of theassembly, it is also possible to obtain better results and use thistechnique in a larger number of cases. The possibility to change thebars without removing the implants also makes it possible to envisage amodification of the device more easily in order to adjust theperformance according to requirements and the results observed.

In other embodiments, the device according to the invention can use oneor more bars 2 comprising in part or all of their length a non-planetransversal bearing surface 21. Said bearing surface is produced by aregion where part of the circumference of the bar comprises a convexitylower than the convexity of the rest of the circumference of the bar. Alower convexity in this case refers to a convexity comprising a greaterradius of curvature. The contact with a plane surface of the clampingscrew 31 or clamping means will then be greater than on a circularcircumference and more reliable.

In one embodiment represented in FIGS. 7 and 8, the device according tothe invention uses one or more bars 2 comprising a transversal bearingsurface 21 showing a face of opposed convexity to the rest of thecircumference, i.e. concave. In this embodiment, the clamping means, forexample the clamping screw 31, comprise a clamping face 310 showing aconvexity in the same direction as the bearing surface 21 of the bar 2.Said clamping surface 310 may in particular show a form of revolutionaround its screwing axis d31, so that said screwing can be carried outwith a progressive approach and a continuous contact on the bar 2.

Depending on the applications, the bar 2 may comprise one or moreregions comprising such a transversal bearing surface 21.

Said bearing surfaces may be produced in several regions, contiguous ornot, distributed along the bar or on only part of this length. Such abar may in this way comprise one or more spherical recesses, or oblongrecesses with a circular cross-section and spherical ends, or in theform of grooves of circular cross-section transversal to the bar.

Said bearing surfaces may also be produced in several parts of the samesection of the bar, i.e. distributed in several different angularpositions around the same point located on the axis of the bar. Such abar may in this way comprise several grooves along its length indifferent angular positions.

Such position variations thus make it possible to produce a small numberof different bar models for numerous anatomical or pathologicalconfigurations, by clamping on the most suitable bearing surface. Thesedifferent clamping point possibilities may also enable easier adjustmentof the longitudinal position of the implants in relation to the bar.Indeed, it is possible to insert the bar into the channel of the implantand hold it there by screwing the clamping screw sufficiently, withoutlocking it. The presence of a tapered recess or a plane, convex orconcave groove makes it possible to move the implant on the bar beforelocking.

In the embodiment illustrated in FIG. 7, the clamping surface 310 andthe bearing surface 21 comprise approximately complementarycross-sections, transversal to the bar 2. Therefore, clamping is carriedout on large contact surface and ensures a good reliability in itself.In this embodiment, the clamping surface 310 may show for example aspherical portion shape. The channel 32 receiving the bar 2 in the bodyof the implant 3 may then comprise an arc-shaped internal wall 320wherein the centre coincides with the centre of the clamping 310 andbearing surfaces 21. In this way, it is possible to modify, around saidcentre, the angular position of the bar in the channel, for example in aslightly offset position 2′, to carry out a rotation or de-rotation toadjust the relative angular position of several implants fixed onto thesame bar. Due to the arc shape of the internal wall 320 of the base ofthe channel 32, said adjustment may be carried out without modifying thedistance of the bar to the clamping screw and therefore there is no riskof untimely locking or unlocking.

In the embodiment illustrated in FIG. 8, the clamping surface 310 of theclamping screw 31 shows a lower convexity than that of the transversalbearing surface 21 of the bar 2. In this embodiment, the clampingsurface 310 may for example show a spherical portion shape. The bearingsurface 21 of the bar will show in this case an arc-shapedcross-section, transversal to the bar, of a radius greater than that ofthe clamping surface 310.

While obtaining a large contact surface between the clamping screw andthe bearing surface, such a configuration makes it possible carry out arotation or de-rotation of the bar to adjust the relative angularposition of several implants fixed onto the same bar. It is possible inthis case to use a channel 32 wherein the internal wall 320 iscomplementary to the bar, the angular adjustment of the bar then beingpossible around the axis of the channel or bar.

In this way, the invention relates to an osteosynthesis device,particularly for the spine by means of internal implantation, comprisingfirstly one or more bars 2 used to support or move the spine, andsecondly at least one implant 3 connecting the bars and the vertebrae V,said implant comprising firstly bone anchorage means attached to thebody of said implant and secondly fixation means for said bars, saidfixation being carried out by clamping means 31 clamping said baragainst the internal walls 320 of a channel 32 formed in said body ofthe implant 3, characterized in that said bars comprise a transversalbearing surface 21 on at least part of their length, said transversalbearing surface being produced by a section of said bars comprising atleast one flat part or part of lower or opposed convexity in relation tothe rest of said section.

According to one embodiment, the transversal bearing surface 21 of thebar is composed of at least one concave shaped face, showing the shapeof a concave recess or a groove.

According to one embodiment, the clamping means comprise a convexsurface which is supported on the recess or groove of the bar 2, thusensuring good clamping reliability.

According to one embodiment, the transversal bearing surface of the baris composed of at least one face in the form of a flat part 21.

According to one embodiment, the clamping means comprise a plane surface310 which is supported on the flat part 21 of the bar 2, thus ensuringgood clamping reliability.

According to one embodiment, the clamping means 31 comprise a joint 311,for example a ball joint, between their main body and the plane surface310 supported on the flat surface 21 of the bar 2, enabling a planesupport even if the flat part of the bar forms a non-null angle a31 witha plane perpendicular to the axis d31 of the clamping means.

According to one embodiment, the bars 2 comprise at least one of theirends a part with no flat part or transversal bearing surface over adetermined length, said part with no flat part forming a shoulder 23capable of co-operating with the shape of the implant or clamping meansto act as a longitudinal stop on the bars, thus making it possible toreduce the length protruding from the implants 3 located at their endsand therefore to reduce the size of the device.

According to one embodiment, the support bars 2 comprise on a part oftheir length a plane face 22 co-operating with an internal wall 320 ofthe channel of the implant forming a plane surface to carry outpositioning and stable centering of the bar in said opening.

According to one embodiment, the plane surface 320 of the channel 32 ofthe implant can form a non-null angle b with a plane perpendicular to 30the axis d31 of the clamping means, said angle b being oriented in thedirection where the clamping means are to be loosened d31 to enable thebar to come out d32 of the base of the channel.

According to one embodiment, the approach distance of the clamping means31 and the dimensions of the channel 32 of the implant are sufficientlylarge to receive bars of different thicknesses e1, e2 with the sameimplant model 3, it being possible to compensate for said differences inthickness with a variation in the position of the clamping means inrelation to the opposite wall 320 of the channel.

According to one embodiment, the clamping means 31 are located on onlyone of the two edges of the channel 32 of the implant 3 and can thus bepre-fitted in the implant without obstructing the insertion of the bar 2during the surgical intervention.

According to one embodiment, the implant 3 receives the bar 2 in achannel 32 wherein the opening comprises an extension direction d32forming a non-null angle a with a plane perpendicular to the axis d31 ofthe clamping means, said angle a being oriented in the direction wherethe clamping means are to be loosened d31 to enable the bar to come outd32 of the base of the channel.

According to one embodiment, the edge of the channel opposite theclamping means forms a nose 321 which prevents the bar 2 from coming outof the channel 32 perpendicular to the axis of the clamping means 31,for example under the effect of vibrations, wear or crushing of thedifferent surfaces in contact.

According to one embodiment, the clamping means 31 are composed of aclamping screw mounted into a threaded hole passing through one of theedges of the channel 32 receiving the bar 2 in the implant 3.

According to one embodiment, the bone anchorage means of the implant arecomposed of a tapered and threaded part 33 that can be screwed into avertebra V, for example into a pedicle.

According to one embodiment, the axis d31 of the clamping screw isapproximately parallel to the symmetrical axis d33 of the bone anchoragemeans of the implant.

According to one embodiment, the top edge of the channel 32 comprisingthe clamping screw 31 is retracted at the symmetrical axis d33 of theimplant in relation to the bottom edge of the channel, limiting the sizeof the implant in the part-opposite the bone anchorage means.

According to one embodiment, the nose 321 formed by the bottom edge ofthe channel 32 protrudes by a determined distance r1 in relation to thetop edge moving from the axis d33 of the implant and protrudes by adetermined distance r2 in relation to the base 320 of the channel, alongthe axis of the clamping screw and in the loosening direction d31.

According to one embodiment, the bone anchorage means of the implant arecomposed of a curved part that can be attached to a shape disorderpresent on a spinal component.

According to one embodiment, the device can be used to perform spinalosteosynthesis in exclusively internal implantation.

The invention also relates to a method to prepare such an osteosynthesisdevice, characterized in that it comprises a step consisting ofinserting the clamping means 31 into the implants 3, said step beingcarried out prior to the surgical intervention.

It should be clear to those skilled in the art that the presentinvention allows embodiments in numerous other specific forms withoutleaving the scope of the invention as claimed. As a result, the presentembodiments must be considered as illustrations, but may be modified inthe field defined by the scope of the claims attached and the inventionmust not be limited to the details given above.

1. An osteosynthesis device comprising: a bar comprising a generallyrounded portion having a substantially flat longitudinal bearing surfaceextending substantially parallel to a longitudinal axis of the bar alongat least a portion of a length of the bar; and an implant having alongitudinal axis and comprising a channel having an opening along aside of the implant sized to admit the bar in the channel and a clampingwall having a clamping surface complementary to the substantially flatlongitudinal bearing surface of the bar, the clamping surface forming anon-zero angle with the longitudinal axis of the implant, and a clamphaving a fully open position providing sufficient clearance in theopening of the channel to admit the bar in the channel, a partially openposition in which the bar is loosely retained in the channel, and aclamping position in which the bar is completely clamped to the clampingwall of the channel.
 2. An osteosynthesis device comprising: a barcomprising a rounded surface and a transversal bearing surface, therounded surface and the transversal bearing surface extending a firstlength longitudinally along a first portion of the bar, the bar having afirst cross-sectional circumference along the first portion of the bar,the first cross-sectional circumference of the bar having a convexityalong the rounded surface of the bar, and the transversal bearingsurface being selected from the group consisting of surfaces that aregenerally flat in the cross-sectional circumference, surfaces that havea convexity less than the convexity along the rounded surface of thebar, and surfaces that are concave in the cross-sectional circumference;and an implant comprising a body, a bone anchor, a clamp movablyengageable with the body of the implant, the clamp comprising a bearingsurface configured substantially complementary to the transversalbearing surface, and a channel having an opening along a side of theimplant configured to receive the first portion of the bar with theclamp at least partially engaged with the body of the implant.
 3. Deviceaccording to claim 2 wherein the transversal bearing surface of the baris concave in the cross-sectional circumference and the bearing surfaceof the clamp is convex.
 4. Device according to claim 3 wherein thetransversal bearing surface of the bar has a first radius of curvature,the bearing surface of the clamp has a second radius of curvature, andthe first radius of curvature is greater than the second radius ofcurvature.
 5. Device according to claim 2, wherein the transversalbearing surface of the bar is flat in the cross-sectional circumferenceand the bearing surface of the clamp is flat.
 6. Device according toclaim 2 wherein the bearing surface of the clamp is articularly disposedby a joint.
 7. Device according to claim 2 wherein the bar has at leastone end portion comprising a longitudinal stop.
 8. Device according toclaim 7 wherein the at least one end portion does not have a transversalbearing surface, and the longitudinal stop comprises a shoulder formedat a junction of said end portion with the first portion of the barhaving a transversal bearing surface.
 9. Device according to claim 2wherein at an internal wall of the channel of the implant comprises aplanar surface configured complementary to a planar face disposed on thebar.
 10. Device according to claim 9 wherein the clamp has an axis andthe planar surface of the implant forms a non-null acute angle with aplane perpendicular to the axis of the clamp, said angle being orientedtoward the opening of the channel.
 11. Device according to claim 2wherein the clamp has an approach distance, and the approach distance ofthe clamp and the dimensions of the channel of the implant aresufficiently large to receive bars of different thicknesses.
 12. Deviceaccording to claim 2 wherein the channel has two edges, and the clamp islocated along only one of the two edges of the channel.
 13. Deviceaccording to claim 2 wherein the clamp has an axis and a looseningdirection, and the opening of the channel defines an extension directionthat forms a non-null angle with a plane perpendicular to the axis ofthe clamp, said angle being oriented in the loosening direction of theclamp.
 14. Device according to claim 2 wherein the clamp has an axis,the channel has an edge opposite the clamp, and the edge of the channelopposite the clamp forms a nose configured to retain the bar in thechannel along a direction perpendicular to the axis of the clamp. 15.Device according to claim 2 wherein the channel has at least two edges,and the clamp comprises a clamping screw mountable in a threaded holepassing through one of the edges of the channel.
 16. Device according toclaim 2 wherein the bone anchor of the implant includes a tapered andthreaded part configured to be screwed into a vertebra.
 17. Anosteosynthesis device comprising: a bar comprising a generally roundedportion having a substantially flat longitudinal bearing surfaceextending substantially parallel to a longitudinal axis of the bar alongat least a portion of a length of the bar; and an implant comprising achannel having a clamping wall and an opening along the side of theimplant sized to admit the bar in the channel, and a clamp having asubstantially flat clamping surface complementary to the substantiallyflat longitudinal bearing surface of the bar, the clamp having a fullyopen position providing sufficient clearance in the opening of thechannel to admit the bar in the channel, a partially open position inwhich the bar is loosely retained in the channel, and a clampingposition in which the bar is completely clamped to the clamping wall ofthe channel.
 18. The osteosynthesis device of claim 17 in which the barcomprises plural substantially flat longitudinal bearing surfacesextending substantially parallel to the longitudinal axis of the baralong at least a portion of the length of the bar.
 19. Theosteosynthesis device of claim 18 in which the clamping wall of thechannel is complementary to one of the flat longitudinal bearingsurfaces of the bar.
 20. The osteosynthesis device of claim 17 in whichthe clamp comprises a clamping screw disposed in a threaded hole of theimplant.